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<i>36C3 preroll music</i>

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Herald-Angel: Good. Ladies and gentlemen,
we have here a talk by Sebastian Staacks.

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Do I pronounce this well?
Sebastian Staacks: Yes.

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Herald: Yes. Staacks. Staacks. [In German]
Ich musste das mal in Deutsch sagen. And

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he's related to the University of Aachen.
He did a PhD physics. And he was in a team

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that developed a fantastic application, as
I mentioned earlier on. He developed the

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app phyphox. Do I pronounce this well?
Staacks: I would say phi-phox, physical

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phone experiments.
Herald: Okay. Yep. Of course. I'm sorry.

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I'm not in that kind of department. But
this application actually gives you all

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the possibilities off your the usage, off
your smart smartphone. Really? Really

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extending certain borders, to my opinion.
So please give a warm, warm welcome here

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to Stefan.

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<i>Applause</i>

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Stefan: Thank you. Thank you for the
introduction and welcome everybody to my

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talk. Yeah. As you've just heard, I'm a
physicist from the RWTH Aachen university

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where I developed the app phyphox. Phyphox
is an app for those of you who do not know

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it already. That uses the sensors in the
smartphone for physics teaching. So the

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idea is that students can use their own
phones to do experimentation in class, in

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the lecture hall. So for schools and
universities. I should explain. That in

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contrast to some other talks by me. This
one will not be that much about education

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because it is the chaos communication
Congress and this is the hardware track

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here. So I tried to tell you a little bit
about the app, a little bit about the

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sensors that we have on our phones and.
Yeah. Would we love to get in touch with

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some, especially people from maker
community and from open source communities

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to find some connections, how he can get
many open source projects together?

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Because I've got so much feedback from
teachers and I think I could also use some

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feedback from other developers as well. So
I would like to start with a short

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explanation of what we actually do. So
yes, I said I come from a university and

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there we have this introductionary lecture
for physics students, which is called

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experimental physics one. And it's typical
lecture. Looks like this. We have a fancy

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new lecture hall by now, but the situation
is the same. We've got 300 I think 370

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students this year sitting in a lecture
hall and doing no experimentation at all.

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There's only one guy experimenting and
that's the professor. And the students are

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sitting there and enjoying the whole show
like they would enjoy a YouTube video and

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maybe they are mildly amused if something
goes wrong. OK. And we thought we could

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change this by using the sensors in the
smartphones. We're not the first ones with

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the idea to use the sensors there, but for
some reason we decided to write our own

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app, which turned out to be quite
successful then. So in contrast to the old

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version where students just had to look at
and I'll get the assignments where they

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can do their own experiments with their
own measurement devices. And to give you

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an idea of what this looks like. I would
like to start with the first experiment.

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Which is about centrifugal acceleration or
centripetal acceleration depending on your

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preferred frame of reference. So the idea
is from a rotation movement, we want to

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measure the radial acceleration as a
function of the angular velocity. So the

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rotation rate. To do this we take a
regular smartphone, this is an iPhone 8 in

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this case and we put it into a salad
spinner. Okay. We get some rotation in

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there and whoops let me just place it in
there. Sound is not important, but it

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sounds nice. I have been told. So here we
get the live data from the phone already.

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Acceleration on the y axis and angular
velocity on the x axis. If the salad

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spinner is actually moving. And what you
see is the faster I rotate the spinner,

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the farther on the right you get your data
because that's angular velocity and also

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the radial acceleration increases. If I'm
not going too fast because then I do not

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get any data at all anymore. Let's slow
down again and we can fill up the gaps

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there by going really slow and filling up
this path. And in the end, if so, who here

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has a physics background some more than
expected. Great. Because those of you who

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just raised their hands would not be
surprised that we expect a square

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relationship between the radial
accaleration and angular velocity. Those

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of you who do not know will believe me
from this plot where on the x axis we've

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got the angle of velocity squared and on
the y axis the radial acceleration we get

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a straight line and that's what you would
expect. So besides the physics, because

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this is not that much about the physics.
This is a simple experiment all our

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students could do and actually they ge, we
gave them this assignment. We gave them

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also a bonus point if they created a
video. Don't worry. Their consent to that

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we use the video was not related to the
point, they first got the point and then

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we asked for their consent to use the
video. And we learned two things from

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these videos. A Our students do not really
have salad spinners. they've got bicycles

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and office chairs, but b and that was the
most important thing. It looks like I

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mean, these are from this year where we
got almost 100 videos they we actually

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could trigger them to go out, search for
something where they've got the

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rotationary movement and they could repeat
this experiment. Ok. Another example which

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actually changed just the course of the
lecture a little bit is a situation where

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we first give the assignment before we
actually let them, before we actually

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discuss the theory behind this, which
means in this example, this is a little bit

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older because we did not get there yet this
year, we assigned our students to build

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string pendulums. They look very similar
because we were very precise about how

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they should build them. And then we had an
online form where they could submit the

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length of their pendulum and the frequency
they received from it that they measured

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with the pendulum. They should do this for
three different cases. And the idea was

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that we did this assignment long before we
discussed the pendulum in the lecture so

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that they have got a little bit of
research experience. And after we

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collected all the data from them, then the
lecture would discuss the pendulum. So the

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physicists were there now. We do a small
angle, approximation solving differential

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equation. All this theory stuff. And in
the end we were done, we could tell our

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students, well, we do not have to do this
experiment on stage. Now, because all of

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you did this experiment and we simply can
compare the theory that we just arrived

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with your data. And it worked out quite
well. So you see most of the white points,

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which is the data from the students
matches the theory, which is the orange

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line, except maybe for those three who
should proceed on a career of theoretical

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physics. But yeah, so this is all
something got nice feedback from and this

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is in principle how we use the app and
what it's designed for. There are also of

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course many applications in school by now.
More teachers use this in school than we

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use it at the university. So we take this
into consideration as well. But that's the

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reason that I am standing here talking
about the sensors in the smartphone.

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That's the reason that I am trying to
access them. so let's have a look at what

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sensors we actually have in our phone. I
think the first one that most of you would

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think often talking about sensors besides
obvious stuff like the microphone would be

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the accelerometer. So I think yeah, I
think I first explain how the

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accelerometer works. OK, so the
accelerometer in your phone is actually a

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so-called MEMS device. MEMS is M E M S
stands for Micro Electrical Mechanical

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System and it looks roughly like this.
It's a simplification. If you search for

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actual MEMS devices, simply search for M E
M S and accelerometer and you find some

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pictures. They usually are a little bit
more complicated, although the

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accelerometer is not that much more
complicated. It consists of an orange

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case. Yeah, well so far so obvious, but
also two contacts. The blue and the red

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one and important part is this silvery
structure here or the metallic structure

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which is under etched its bit hard to see
on this picture, but it's actually

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floating. It's only attached to the sides,
you see light in between here. So if you

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move around, the accelerometer the inner
path, can actually move. So let's do this.

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So at each point where the device is extra
riding in one direction or the other

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direction, due to inertia the that the
metallic part in here is distorted, moved

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into one direction and we can measure the
amount by which it is deflected by this

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movement with the two contacts by
measuring the capacity between these

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structures. So that's the principle of the
accelerometer. One thing to mention at

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this point is that it's in the sense of
physics. It does not really only measure

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acceleration. It measures acceleration you
see in this image of the device

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accelerating. We get some data, but if you
imagine we take this device and rotate it

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like this, then of course you also get a
deflection of the of the metallic part by

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gravity. So gravity is pulling it down as
well. And that's the main reason the

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accelerometer is in there because the
developers and manufacturers of the phones

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are not really interested in measuring
acceleration, at least there aren't that

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many use cases for it. But instead, what
they want to have is an indication on

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which direction is down or which direction
is up. So when you rotate the screen of

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your phone, actually they can rotate the
content of the phone as well or with this

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you can also then control video games by
tilting your phone and stuff like this.

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Because gravity also deflects the
accelerometers. Earth's acceleration,

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which you try to avoid because from
didactic point of view, this is a

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nightmare to distinguish these both. But
the point is that we can detect rotations

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like this and this is pretty much in every
phone. I mean, this is not really a

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statistic. This is just the first pie
chart we have about availability. I have

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never encountered a single phone or tablet
that does not have an accelerometer. So if

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anyone ever encountered some special
device, some very unique device that

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doesn't have one. Let me know because I
would be interested in this at least. I do

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not know of any device on which phyphox
actually runs, which doesn't have an

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accelerometer. A bit more interesting is
which data rate we can achieve. So most

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accelerometers have several hundred
samples per second. Actually the fastest

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ones go up to 500 hertz and but there are
also many devices that only do one hundred

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hertz That's 100 values per second. These
are mostly the cheaper Android devices and

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all the iPhones. So I think the internal
accelerometer will do more on an iPhone.

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But I have to admit, at some point I can
understand why they might limit this. But

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on an iPhone, you get 100 hertz. That's
the limit. From the API, what you can get

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there. But this is actually quite a lot. I
will later see what we can do with this.

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And one other point about calibration of
this thing. Actually for all the sensors

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to get reasonable units from the system so
the acceleration is given in meter per

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square second. I just realized that if I
get the units, that's something I would

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really tell my students. But yeah. So on
the x axis, it's a meter per square second

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and you see that as a wide range of values
that you get there. So this data is from

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our sensor database. I would mention it
later as well. This is contribution from

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our users what data there this. This only
absolute value that we get from resting

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phones and we would expect nine point
eight one meter per square second for

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earth acceleration. There are some local
variation, but not on that scale. So do

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not expect your sensors to be well
calibrated. Also, if you've got any app

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that tells you you can push a single
button and then calibrates your sensor,

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don't trust it. It's not that simple.
These sensors may have different errors on

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each axis. They're all 3D sensors we've
got an X, Y and z axis. These errors can

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be linear errors so you have to multiply a
correction. It could be an offset. So it

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would have to add an correction. And on
top of this, the entire device could be

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tilted within your phone. OK. So actually,
if you look into the data sheets of the

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accelerometer, they have some tolerance on
how much they might already be shifted or

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rotated within the package. And when
soldering it into the phone, I would

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assume there will be an additional error.
I've seen so many different errors on

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different phones. It's not that easy to
simply calibrate that. But let me give you

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an example of what you can do with it. Or
just a quick look first. So we see in our

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app. Yeah. So this is phyphox. OK. Thank
you. Got this. You have an entry

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acceleration with G. That's the extra raw
data from the sensor or as raw as we get

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it. If I started you see if I shake it,
you get some readings there. It's fast.

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It's already great. You can apply to
pendulum and measure the acceleration of

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the pendulum like this. But something I
want to demonstrate is that we can also

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get the frequencies from this data by
doing a fourier transform and calculating

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the frequency spectrum of this exploration
data and to demonstrate this I brought a

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little device a old hard disk drive. It says
it's broken, but it's still rotating and

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that's important part for us. So if I
place my phone on top of it, start the

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measurement. Turn on the hard disk drive.
And then you see a peak showing up in the

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spectrum and it settles at 120 hertz. If
you don't believe me. Unfortunately, we

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don't have a camera here right now. You
can later have a look. It's supposed to

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run at seven thousand two hundred RPM,
which is 120 hertz. We can even get a time

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resolution of this. So if I turn it off
again, you see how the frequency drops

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down. And if I turn it on again. There it
comes up again. OK. So this an example of

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what you can do. It's great for students
that can check if the washing machine at

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home is working properly or they can
check other things. But usually I do not

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like to bring washing machines to talks.
So I used the hard disk drive here. One

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other thing you might have noticed before
is that we've actually got acceleration

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with G and acceleration without G. The
second one is actually a sensor that

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removes Earth's gravity. So if I start the
one with G, you will notice that down here

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on the Z, the axis you still have the 9.81
meter per square second, which is great

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because if i rotate the phone. This
contribution goes to other axis and we can

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determine the orientation of the phone.
But this is bad actually for dedactics

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because actually the phone is resting.
It's not moving at all. There's no

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velocity involved. There's no
acceleration. So luckily, there's also an

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acceleration without G, which gives us
roughly 0 an all axis unless I actually

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accelerate this thing. Problem with this
is this is only a virtual sensor. This is

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a sensor that's fusing the data from the
accelerometer with an additional sensor

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like the gyroscope. So we can actually
distinguish between rotating the phone or

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accelerating it in one or the other
direction. Usually you only get

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acceleration without G. If you also have a
gyroscope in your phone, I've seen two or

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three devices that offer you acceleration
without G, even though they don't have a

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gyroscope. This case, don't trust them.
This is merely guessing. OK. So it's. They

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probably have only low frequency filter
on top of this, or they're averaging out

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your movement and this doesn't really work
for anything. Yeah so that's the

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accelerometer or one other thing I want to
mention is if you look into the API to

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access the sensors yourself for some
reason you will notice acceleration

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without G is usually called linear
acceleration in our app since it's made

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for teaching. We decided to call it with
and without G. So if you find

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accelerometer, that's the one with G and
linear acceleration is the one without G.

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If you look at other apps or the API.
Okay. Next up, I already mentioned this

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one is a gyroscope. If you have, some
physics background. Then when you think of

206
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a gyroscope, you're thinking of a device
that's spinning fast so it has some angular

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momentum and then usually you want it to
be heavy and to have the weight at the

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large radius. We've got a strong moment of
inertia so that you get when it's spinning

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fast, a strong, angular momentum and due
to the conservation of angular momentum.

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These spinning devices can keep an axis
regardless of rotating the frame around

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it. That's what I was thinking about, a
gyroscope of what I think is a gyroscope.

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When you just give me the term out of
context, of course, a heavy, huge, fast

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spinning device is the last thing you want
in your phone. So that's not what's meant

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00:17:38,179 --> 00:17:42,660
with the gyroscope when people are talking
about gyroscopes in your phone. Instead

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there again you have a MEMS device. So
again, micro electromechanical system. You

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notice this looks almost exactly like
accelerometer. If you look for real

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devices, those are actually much more
complicated because they need some

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specific geometry to make sure that they
do not act like an accelerometer. But the

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00:18:02,460 --> 00:18:08,289
principle is easy to explain with the same
geometry. So we again have this floating

220
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metallic part and we've got 2 contacts. So
again, we've got a part that can wobble in

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this direction here. But on top of this,
we've got the motion that's perpendicular

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to this. So this is now not depicting the
motion of your phone, but this is

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depicting a vibration that the gyroscope
does by itself all the time. So there are

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different ways to build them. Some have a
rotary motion, some have this linear

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motion. Also, the way to create this
motion makes this device so much more

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complicated. But in principle, it's a
similar structure which is vibrating forth

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and back and now if you add rotation to
it. It's a little bit hard to see it as

228
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it's rotating the inner part now suddenly
gets deflected. That's changed, right?

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Frame of reference. So let's get the
camera in sync with this device. What you

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now see is that the inner part is moving
left and right, although the device itself

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is only moving up and down. And the reason
is I don't want to deduce it entirely

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here, but most of you probably have heard
of it. This is the Coriolis effect. So,

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yes, in fact, your phone is determining
the rotation rate of your phone, not the

234
00:19:14,649 --> 00:19:18,460
actual angle, but the rotation rate or
angular velocity due to the coriolis

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00:19:18,460 --> 00:19:24,710
effect, which is just mind blowing if you
do some of the calculations. There are

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some manufacturers on the Internet which
claim that they can detect a movement of

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00:19:32,200 --> 00:19:36,669
the order of magnitude of a single atom.
And I believe them because we use similar

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00:19:36,669 --> 00:19:41,799
structures in solid state physics. So
that's possible. If you want to try it,

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00:19:41,799 --> 00:19:47,080
just turn on the gyroscope on your phone.
And do slight rotation like this, which is

240
00:19:47,080 --> 00:19:52,980
about the Z axis, one perpendicular to the
display, you can detect really slow

241
00:19:52,980 --> 00:19:58,090
rotations with this. And think about the
fact that this is done using the coriolis

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00:19:58,090 --> 00:20:04,480
effect and it's just mind blowing I think.
So this sensor is a bit more available.

243
00:20:04,480 --> 00:20:10,370
Actually, almost 80 percent of the phones
have them. This has become significantly

244
00:20:10,370 --> 00:20:15,370
more since Pokémon GO. The reason is
when this game came up, suddenly people

245
00:20:15,370 --> 00:20:19,039
noticed that there's a device called the
gyroscope. And if it's not present, they

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00:20:19,039 --> 00:20:22,540
did not have this AR mode where you can
actually take pictures of the nice cute

247
00:20:22,540 --> 00:20:27,649
Pokémon and so on. So this is when the
many people noticed it and the

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00:20:27,649 --> 00:20:32,320
manufacturers decided, OK, let's just
throw in the gyroscope as well, because

249
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it's not that expensive, in fact, usually
it's on the same chip as the

250
00:20:35,440 --> 00:20:39,289
accelerometer. Then they're sold as one
thing it's an IMU - Inertia Measurement

251
00:20:39,289 --> 00:20:45,389
Unit not important at home, but so it's
quite a common thing. And the sensor rates

252
00:20:45,389 --> 00:20:50,809
look pretty much the same. You mostly
notice the dip in the 100 hertz regime

253
00:20:50,809 --> 00:20:54,610
because those are the real cheap phones,
which then also don't have a gyroscope.

254
00:20:54,610 --> 00:20:59,620
But most of the phones achieve higher
rates. Again, since we were laughing

255
00:20:59,620 --> 00:21:05,512
before the iPhones also are here again at
the 100 hertz. Wouldn't make sense to have

256
00:21:05,512 --> 00:21:10,809
the gyroscope faster at this point. Yeah,
but that's it about the gyroscope you've

257
00:21:10,809 --> 00:21:16,460
seen it in action in the salad spinner.
And that's one of the sensors you do not

258
00:21:16,460 --> 00:21:21,950
really see that often directly, but were
just mostly there to assist other things

259
00:21:21,950 --> 00:21:28,460
that you do where you need to get smooth
motion like controlling games, AR . And

260
00:21:28,460 --> 00:21:34,409
actually removing the Earth's acceleration
from the accelerometer. Next up is a

261
00:21:34,409 --> 00:21:39,399
magnetometer, which I think is a more
obvious sensor because that's your compass

262
00:21:39,399 --> 00:21:45,350
in your device. So when you're doing
navigation with a GPS in your car, it's a

263
00:21:45,350 --> 00:21:49,539
simple thing. GPS gets a position, you get
a sequence of position as you going and

264
00:21:49,539 --> 00:21:52,480
from the sequence of the positions you
get, the direction you're moving in your

265
00:21:52,480 --> 00:21:56,530
car and your phone is attached to the
dashboard at least i hope so. So it's

266
00:21:56,530 --> 00:21:59,419
pointing in the same direction you're
moving, everything's obvious. But if

267
00:21:59,419 --> 00:22:04,259
you're standing on an open space looking
for not sure a train station or anything

268
00:22:04,259 --> 00:22:07,710
and you wondering which direction you want
to go from point of view of GPS, it's

269
00:22:07,710 --> 00:22:11,929
always the same position it doesn't get an
orientation. You need a compass, which is

270
00:22:11,929 --> 00:22:17,350
the magnetometer. How do we get a compass
on your phone? This is usually a hall

271
00:22:17,350 --> 00:22:23,210
sensor. A hall sensor is in principle just
a conductor with charge carriers so these

272
00:22:23,210 --> 00:22:27,759
are the nice shiny white balls here
drifting from one side to the other so

273
00:22:27,759 --> 00:22:31,860
it's just an electric current. And if you
apply a magnetic field to an electric

274
00:22:31,860 --> 00:22:36,759
current or to any electric charge, then
there is an effect. You might know from

275
00:22:36,759 --> 00:22:41,039
school, which is called the lorentz
effect. So there is a charge going one

276
00:22:41,039 --> 00:22:44,710
direction, you get the magnetic field
perpendicular to this and then the charge

277
00:22:44,710 --> 00:22:50,579
is deflected into a direction
perpendicular to the flying direction. And

278
00:22:50,579 --> 00:22:54,539
yeah, that's lorentz effect the older
guys, of you would know it from CRTs. If

279
00:22:54,539 --> 00:22:59,610
you bring a magnet close to a CRT, the
entire image is messed up due to this

280
00:22:59,610 --> 00:23:05,980
effect. And that's what we're using in
hall effect sensor or hall sensor you've

281
00:23:05,980 --> 00:23:12,059
got this electric current and if you bring
a magnetic field close to it, the charge

282
00:23:12,059 --> 00:23:17,190
carriers are deflected to one side or the
other. And therefore, if you're measuring

283
00:23:17,190 --> 00:23:22,629
the voltage perpendicular to the flow of
the count, you get. Yeah. You get an extra

284
00:23:22,629 --> 00:23:26,230
voltage that's proportional to the
magnetic field. That's the hall effect.

285
00:23:26,230 --> 00:23:32,399
That's how your phone is able to determine
the magnetic field. This one is even more

286
00:23:32,399 --> 00:23:37,299
common than the gyroscope simply because
it's used for navigation and people start

287
00:23:37,299 --> 00:23:42,330
to notice if it's not. If it's not present
and they do not get an orientation in the

288
00:23:42,330 --> 00:23:49,900
navigation software. But the actual rate
of the sensors is much slower than for the

289
00:23:49,900 --> 00:23:54,710
accelerometer. Most of them are running at
100 Hertz. It will be important in two

290
00:23:54,710 --> 00:24:00,440
more slides. Besides that, there's not
that much strange about the availability

291
00:24:00,440 --> 00:24:05,759
of this, but it's extremely sensitive
because it's supposed to measure Earth's

292
00:24:05,759 --> 00:24:10,070
magnetic field. Earth's magnetic field has
the strength around 50 micro Tesla. This

293
00:24:10,070 --> 00:24:15,649
is not much actually if ever carried the
magnetic magnet with you. Did you fear of

294
00:24:15,649 --> 00:24:19,919
some force from the Earth's magnetic
field? Of course, it didn't need to build

295
00:24:19,919 --> 00:24:23,110
some compass where the needle is floating
on something like this to actually get a

296
00:24:23,110 --> 00:24:28,279
rotation. It's a very weak field and
that's good news and bad news as well,

297
00:24:28,279 --> 00:24:32,080
because on one hand, it's very sensitive.
downside is it's very sensitive. Which

298
00:24:32,080 --> 00:24:36,069
means it saturates very early. If you want
to measure the magnetic field of an actual

299
00:24:36,069 --> 00:24:41,769
magnet. Don't even try it will saturate
right away. You do not get anything to

300
00:24:41,769 --> 00:24:47,749
demonstrate how how sensitive this
actually is. I've brought a flashlight, so

301
00:24:47,749 --> 00:24:55,091
a very simple one. And I switch to a modus
where we've got an s.o.s signal. That's

302
00:24:55,091 --> 00:25:00,679
coming up, a point in this direction and I
place it next to the magnetometer in my

303
00:25:00,679 --> 00:25:05,909
phone. And yeah, you see right away so
much of his seeing the lights are pointing

304
00:25:05,909 --> 00:25:09,999
in this direction. You see the s.o.s
signal popping up in the magnetic field

305
00:25:09,999 --> 00:25:14,629
reading simply because of the current
going through the LED. So that's what we

306
00:25:14,629 --> 00:25:17,909
call an Oersted-field. This is just the
typical magnetic field you get from any

307
00:25:17,909 --> 00:25:22,739
current flowing. So I stop it. We got a nice
SOS signal over there. Three short, three

308
00:25:22,739 --> 00:25:31,090
long and three short signals. And it's just
coming from this simple flashlight. And

309
00:25:31,090 --> 00:25:36,629
this is also a good indicator on how
sensitive this thing is. I mean, if you

310
00:25:36,629 --> 00:25:43,580
place your phone in a case with a magnetic
some magnetic closing mechanism, compass

311
00:25:43,580 --> 00:25:47,259
wouldn't work anymore. If you're not
careful when paying your clothes and you

312
00:25:47,259 --> 00:25:51,750
place your phone on the big magnet that
removes the theft protection from the

313
00:25:51,750 --> 00:25:55,860
clothes, something in your phone would get
magnetized and would certainly be stronger

314
00:25:55,860 --> 00:26:01,110
than Earth's magnetic field. For the rest
of the day, your compass would be pointing

315
00:26:01,110 --> 00:26:06,740
in the wrong direction. Okay. Luckily,
usually the phones are able to notice this

316
00:26:06,740 --> 00:26:11,999
and they recalibrate the phone to simply
subtract any constant fears. That again is

317
00:26:11,999 --> 00:26:15,259
bad. If you want to do absolute
measurements because you have not much

318
00:26:15,259 --> 00:26:22,700
control over the recalibration mechanism,
you can access the raw data value. So if

319
00:26:22,700 --> 00:26:27,039
you folks there's a checkmark where you
can disable the calibration, but then you

320
00:26:27,039 --> 00:26:30,850
have to do everything by hand. You will
certainly have some background that's

321
00:26:30,850 --> 00:26:34,980
annoying. And one other thing, you should
also take care and notice where your

322
00:26:34,980 --> 00:26:38,929
actual magnetometer is because in most
phones it's on top left corner, top right

323
00:26:38,929 --> 00:26:44,100
corner, top center. And this Pixel 3 is a
very strange one. It has it on the right

324
00:26:44,100 --> 00:26:48,919
hand side, but it's never dead center. I
think because of all the currents in the

325
00:26:48,919 --> 00:26:53,360
phone, I mean, you're charging your
battery with three amps. How much you

326
00:26:53,360 --> 00:26:57,330
charge them now? This would yield a
stronger field than a flashlight and you

327
00:26:57,330 --> 00:27:03,120
would see it in the magnetometer again.
Now for what you can do with this. So as

328
00:27:03,120 --> 00:27:07,490
little homework for all of you who came by
train yesterday, when I came here on the

329
00:27:07,490 --> 00:27:13,379
ICE, I turned on the magnetic spectrum,
the same thing as the acceleration

330
00:27:13,379 --> 00:27:17,279
spectrum you just seen. And when you're
doing it on train, you would see a peak at

331
00:27:17,279 --> 00:27:24,450
16.6 hertz. It might depend on your actual
seat. You might move it around a little

332
00:27:24,450 --> 00:27:31,190
bit. But so far I usually always saw this
peak. This is the electrification

333
00:27:31,190 --> 00:27:36,480
frequency of the German railway. So you
can simply check if it's working properly.

334
00:27:36,480 --> 00:27:43,179
You should see 16.7 hertz. Okay. One other
thing that some of you might get in your

335
00:27:43,179 --> 00:27:46,350
head right now, that you could do this
with simple electrical outlets. There you

336
00:27:46,350 --> 00:27:49,590
would get a problem with the rate. So
that's what I mentioned, that the rate of

337
00:27:49,590 --> 00:27:55,799
the sensor is quite important. I also got
something via Twitter yesterday. Just as a

338
00:27:55,799 --> 00:27:58,289
response to the other one, I thought,
well, I was looking for an example like

339
00:27:58,289 --> 00:28:02,489
this for this talk talk, so I just put it
in. This is a measurement of an American

340
00:28:02,489 --> 00:28:07,919
power outlet which is run at 60 hertz. But
this guy is seeing 40 hertz and he was

341
00:28:07,919 --> 00:28:15,990
wondering about this. That's what's called
aliasing. So the alias effect, sort of you

342
00:28:15,990 --> 00:28:19,830
might notice this from computer games.
They usually use it in slightly different

343
00:28:19,830 --> 00:28:25,619
context. The idea is if you're measuring a
frequency that's higher than half of the

344
00:28:25,619 --> 00:28:29,570
data acquisition rate of your sensor. So
this one is runningat 100 hertz like most

345
00:28:29,570 --> 00:28:35,759
of the phones do. Then half of this
frequency is what's called the Nyquist-

346
00:28:35,759 --> 00:28:39,559
frequency. And you notice that the
spectrum goes from zero to the Nyquist-

347
00:28:39,559 --> 00:28:45,499
frequency. This is simple math, not simple
math, but its maths. The roots of the

348
00:28:45,499 --> 00:28:49,309
fourier-transformation, you could say so.
And if you try to detect a frequency

349
00:28:49,309 --> 00:28:53,769
that's higher than this, so an American
power outlet with 60 hertz, actually the

350
00:28:53,769 --> 00:29:00,320
higher frequency is showing up as on the
other side of this upper limit at 40

351
00:29:00,320 --> 00:29:03,309
hertz, even if you go to a higher
frequency, it would shift down further and

352
00:29:03,309 --> 00:29:06,420
further until reaching zero and then it
would shift up again. So if you're

353
00:29:06,420 --> 00:29:13,450
interested in this. Check out some
articles about aliasing. If you're not

354
00:29:13,450 --> 00:29:16,649
that interested in this. Just keep in
mind, if you're measuring frequencies that

355
00:29:16,649 --> 00:29:20,340
are higher than half your data acquisition
rate, you will not see the correct

356
00:29:20,340 --> 00:29:26,840
frequency. OK. Then one of my favorite
sensors, the pressure sensor for this one

357
00:29:26,840 --> 00:29:32,960
I need. Again, the phone. That's not on a
wire. Let me before before I show

358
00:29:32,960 --> 00:29:37,559
anything. Let me demonstrate what it can
do, because that's something I find quite

359
00:29:37,559 --> 00:29:42,250
surprising. Let's turn on the measurement.
By the way, those who are wondering how

360
00:29:42,250 --> 00:29:47,970
this works. There's a function in phyphox,
we call it remote access. It's basically a

361
00:29:47,970 --> 00:29:53,469
web server running in the app which
provides the data so we can simply access

362
00:29:53,469 --> 00:29:59,049
the data on the phone to demonstrate or to
control the measurement. And now here we

363
00:29:59,049 --> 00:30:04,049
see the pressure sensor. Right now, just
mostly noise or what I do now is I hold it

364
00:30:04,049 --> 00:30:07,769
up. And if we wait a few seconds, you
would see that the pressure's actually

365
00:30:07,769 --> 00:30:15,450
dropping. It has dropped far enough. Then
I place it on the ground and the pressure

366
00:30:15,450 --> 00:30:20,190
is rising again. So actually, your phone,
if it has a pressure sensor, has a

367
00:30:20,190 --> 00:30:25,850
pressure sensor that's sensitive enough.
So we turn it off to measure a change of

368
00:30:25,850 --> 00:30:33,279
pressure of a distance like this. OK. And
that's again, when I first tried this, I

369
00:30:33,279 --> 00:30:39,529
repeated this test several times before,
believed it was just not by accident. And

370
00:30:39,529 --> 00:30:43,509
how do they do this? You have got another
device that actually has a cavity. So

371
00:30:43,509 --> 00:30:47,649
below the bluish gray part, there's a
cavity in there which is covered by a

372
00:30:47,649 --> 00:30:52,519
silicon membrane, which is the bluish
part. And if you change the pressure this

373
00:30:52,519 --> 00:30:57,530
simply moves it like you would expect from
a membrane just in small. And to detect

374
00:30:57,530 --> 00:31:02,779
this movement, here is some material on
top of this which changes its resistance.

375
00:31:02,779 --> 00:31:11,950
Or resistivity depending on the strain
created by morphing, dismembering. And

376
00:31:11,950 --> 00:31:15,580
unfortunately, this sensor is not that
much available. So about a third of the

377
00:31:15,580 --> 00:31:19,869
devices that we know of have the sensor.
Of course, there's some bias in there from

378
00:31:19,869 --> 00:31:27,429
the users that submit data to us. This
means that, yes, these are usually the

379
00:31:27,429 --> 00:31:31,739
more expensive devices. So my rule of
thumb is if it's an iPhone, they usually

380
00:31:31,739 --> 00:31:36,159
have the pressure sensor except for the
iPhone SE or some older models. If it's an

381
00:31:36,159 --> 00:31:39,700
Android, if you payed half as much as you
paid for an iPhone, then you have a good

382
00:31:39,700 --> 00:31:47,229
chance that you have to pressure sensor as
well. But OK, that data rates? Yeah.

383
00:31:47,229 --> 00:31:54,581
Varies a lot. So the iPhones, like you
just saw the rate of about 1 Hertz. Most

384
00:31:54,581 --> 00:31:59,440
Android phones are on five, ten or twenty
five hertz. I've never had a device like

385
00:31:59,440 --> 00:32:02,619
this in my hand. It does 100 hertz. I
don't really believe that this makes sense

386
00:32:02,619 --> 00:32:09,720
because I already noticed on my phone that
I think it does 25 hertz. Just handing it

387
00:32:09,720 --> 00:32:15,740
because of the sealed casing introduces
more noise than you can actually use, at

388
00:32:15,740 --> 00:32:20,919
least for these small distances that I use
it for. But you can do other funny things

389
00:32:20,919 --> 00:32:26,489
with this. So this is something I received
by Dianna Cowern. You might know her as a

390
00:32:26,489 --> 00:32:32,259
YouTuber called "The Physics Girl". She
used a pressure measurement on the flight.

391
00:32:32,259 --> 00:32:35,509
It's something you should do anyways,
because that's the way you can figure out

392
00:32:35,509 --> 00:32:39,139
how much air you get to breathe up there.
It's much lower than you might expect.

393
00:32:39,139 --> 00:32:43,659
But she saw something else. So at some
point she saw the drop in the pressure and

394
00:32:43,659 --> 00:32:48,350
increase again. And she asked her
followers, what could this be? And I'm not

395
00:32:48,350 --> 00:32:51,909
asking the audience right now. I just give
you the solution. She wasn't lavatory and

396
00:32:51,909 --> 00:32:56,100
she flushed the toilet. So when water and
air gets sucked out, you can actually

397
00:32:56,100 --> 00:33:01,480
measure this. And then about a month ago,
I found someone else who allowed me to use

398
00:33:01,480 --> 00:33:09,350
his measurement. So this guy, Phillip
Smith, was on an airplane again. But he

399
00:33:09,350 --> 00:33:12,820
did not actually go to the lavatory. He
stayed on his seat and he just checked

400
00:33:12,820 --> 00:33:19,019
when people were flushing the toilet. So
as he sat, there was there were

401
00:33:19,019 --> 00:33:21,610
turbulence. So they couldn't go for a
while. And then there was the rush while

402
00:33:21,610 --> 00:33:27,299
the toilet and he was plotting it. So just
for those of you that came here by plane,

403
00:33:27,299 --> 00:33:31,720
just a hint as a conversation starter next time,
when the guy next to you goes to the toilet and

404
00:33:31,720 --> 00:33:36,570
he comes back, tell him exactly all of the
head to flush the toilet and ask him why.

405
00:33:36,570 --> 00:33:41,950
Okay. And you would enjoy the rest of the
flight. Some other example that we

406
00:33:41,950 --> 00:33:47,519
actually use is measuring the movement of
an elevator. So this is a lift in Aachen.

407
00:33:47,519 --> 00:33:52,250
We have the accelometer which measures the
acceleration of this thing, gets the total

408
00:33:52,250 --> 00:33:56,419
height difference of the elevator from the
again, from the pressure sensor, a

409
00:33:56,419 --> 00:34:01,070
barometer. That's a pressure sensor. And
the velocity of the elevator as well from

410
00:34:01,070 --> 00:34:07,470
the change in height. OK, so next time you
enter an elevator, I want to see you all

411
00:34:07,470 --> 00:34:11,609
to take out your phones and measure the
distance that the elevator is traveling

412
00:34:11,609 --> 00:34:17,320
and the velocity at which it does so. OK.
So these are, in my opinion, most

413
00:34:17,320 --> 00:34:22,200
important sensors, some honorable
mentions. Almost all phones have a light

414
00:34:22,200 --> 00:34:26,450
sensor as well, which controls the display
brightness depending on the ambient light.

415
00:34:26,450 --> 00:34:32,060
Unfortunately, there is no API on IOS
to access this. So if there are apps

416
00:34:32,060 --> 00:34:35,840
that seem to access a sensor like this,
they usually use the camera instead, which

417
00:34:35,840 --> 00:34:39,310
is which also works quite well. But it's
slightly different since the difference

418
00:34:39,310 --> 00:34:44,230
between illuminance and luminance, which I
do not want to go into detail here. And on

419
00:34:44,230 --> 00:34:48,830
most Android phones, they are badly
calibrated or do this so much difference

420
00:34:48,830 --> 00:34:52,590
in the quality of the sensors. We have to
check it on your own phone if it's worth

421
00:34:52,590 --> 00:34:57,381
anything. But it's a bit difficult. This
proximity sensor, which is the one that

422
00:34:57,381 --> 00:35:01,140
turns off the screen when you hold the
phone to your ear when you're

423
00:35:01,140 --> 00:35:04,940
actually doing your call. Sounds
interesting, but unfortunately it only

424
00:35:04,940 --> 00:35:09,130
distinguishes or has I know it
distinguishes between between the near and

425
00:35:09,130 --> 00:35:13,910
far value, which is the difference between
five centimeters. So I do not have that

426
00:35:13,910 --> 00:35:22,180
much use for it. There is the temperature sensor,
maybe if they are officially there, then

427
00:35:22,180 --> 00:35:26,550
they usually come along with the humidity
sensor, but that's the sensors in your

428
00:35:26,550 --> 00:35:30,880
phone. So you should be a little bit
skeptical about this. You're mostly

429
00:35:30,880 --> 00:35:34,650
measuring the heat from your battery or
from your device. They tried to compensate

430
00:35:34,650 --> 00:35:38,400
for this, but that's a difficult thing to
do. So if you actually, one, need a

431
00:35:38,400 --> 00:35:44,070
thermometer, take a thermometer. They're
not that expensive. OK. You might see some

432
00:35:44,070 --> 00:35:49,570
temperature sensors that are not official.
Which phyphhox can pick up. Those are usually

433
00:35:49,570 --> 00:35:54,300
temperature sensors that are part of the
pressure sensor to compensate for

434
00:35:54,300 --> 00:35:58,790
temperature effects. So they're not even
designed to get an outside temperature.

435
00:35:58,790 --> 00:36:06,060
OK. So I wanted to mention this. While the
information about where we got the

436
00:36:06,060 --> 00:36:10,310
information about the sensors from, so in our
App at the very bottom, does this entry

437
00:36:10,310 --> 00:36:17,510
submit to a sensor database which tells
you to leave the phone resting on a table?

438
00:36:17,510 --> 00:36:21,180
It also checks if you're actually doing
this, doesn't let you submit it before it

439
00:36:21,180 --> 00:36:26,920
is happy about the error rate or the
standard deviation of the accelometer. And

440
00:36:26,920 --> 00:36:31,380
if you submit it, we collect the data on
phyphox.org/sensordb and that's

441
00:36:31,380 --> 00:36:35,720
where I got the statistics from so far. So
if you're interested in what a new phone

442
00:36:35,720 --> 00:36:40,750
that you're about to buy can actually do.
Of course we don't give you any guarantee,

443
00:36:40,750 --> 00:36:46,420
but you can check up or check out all the
data, all the phones. At least those that

444
00:36:46,420 --> 00:36:49,500
are already in our database. And of
course, I'm happy if you contribute

445
00:36:49,500 --> 00:36:54,320
statistics about the census in your phone
as well. So you might want to play with

446
00:36:54,320 --> 00:37:02,090
this later. And then finally, the last
thing to finally conclude is some

447
00:37:02,090 --> 00:37:05,730
information on how you can access the
sensors. Of course you can write your own

448
00:37:05,730 --> 00:37:10,400
APP. I think here quite a few who can do
this. Just have a look if you can write an

449
00:37:10,400 --> 00:37:14,130
App. Have a look at the API. They're not
too complicated. It's easy to access the

450
00:37:14,130 --> 00:37:18,290
sensor data. If you're not interested in
designing your own app, but you want to

451
00:37:18,290 --> 00:37:22,220
include sensor data in some other
projects, there are three ways you can use

452
00:37:22,220 --> 00:37:27,130
Phyfox for this, which I want to
introduce, because that's something that's

453
00:37:27,130 --> 00:37:32,280
one of the reasons I wanted to connect
here. Don't hesitate. Phyfox is free. You

454
00:37:32,280 --> 00:37:36,210
can get for free on Google Play and on the
Appstore. And when I say it's free, I mean

455
00:37:36,210 --> 00:37:41,850
it's really free. So it's open source. The
GPL and you can also get an afterwards we

456
00:37:41,850 --> 00:37:48,280
assured of code running on your phone
is the code that you see. And we have

457
00:37:48,280 --> 00:37:53,740
three versions how you can.. At least they
are categorized into three versions. How

458
00:37:53,740 --> 00:37:57,410
you can access the sensor data. First
thing is you can implement something in

459
00:37:57,410 --> 00:38:01,800
Phyfox yourself. So I've got this editor,
visual editor of all file format, which

460
00:38:01,800 --> 00:38:06,490
allows you to take a sensor, place on
mathematics. So this is just adding stuff,

461
00:38:06,490 --> 00:38:11,750
but you can apply a Fourier transform or
anything and then assign it to a graph.

462
00:38:11,750 --> 00:38:16,810
Alternatively, and of course a bit more
powerful. You can have a look at our XML

463
00:38:16,810 --> 00:38:21,370
format, which defines all the experiments.
So actually all experiments to see in

464
00:38:21,370 --> 00:38:25,910
Phyfox are not hardcoded, but they are defined
in our own file format you can edit any of

465
00:38:25,910 --> 00:38:32,640
them to your needs. And when you're done
you can transfer your data with the QR

466
00:38:32,640 --> 00:38:36,740
code. Do not try to scan this QR code just
from your QR code app. You have to scan

467
00:38:36,740 --> 00:38:42,380
it from within Phyfox and if you do,
you'll find a nice little experiment which

468
00:38:42,380 --> 00:38:47,700
uses our file formats to implement a Turing
machine that's counting binary up to 256.

469
00:38:47,700 --> 00:38:51,280
So this is the proof that all file format
actually is Turing complete. So you can do

470
00:38:51,280 --> 00:38:55,620
a lot with it. Okay. I'm not suggesting
that you're trying to implement doom on it

471
00:38:55,620 --> 00:38:59,980
or something like this because you won't
be able to. It's not efficient that way.

472
00:38:59,980 --> 00:39:04,130
It's not designed to be Turing complete.
It just happens to be Turing complete. So

473
00:39:04,130 --> 00:39:08,461
if you want to do something more, you can
connect to Phyfox via a network. You've

474
00:39:08,461 --> 00:39:11,730
seen one example with the salad spinner.
When I said that there is a

475
00:39:11,730 --> 00:39:17,180
a web server running on the App. You can use
this to access the data directly from your

476
00:39:17,180 --> 00:39:21,570
preferred programing language. There's an
example where I'm using Python to read out

477
00:39:21,570 --> 00:39:26,780
the sensor data and control a synthesizer.
So what's running on the web server is

478
00:39:26,780 --> 00:39:31,151
basically a rest API. So yeah. Just visit
our website and learn how to do this. So

479
00:39:31,151 --> 00:39:34,850
you can read out the sensor data of a
network and control your project with it.

480
00:39:34,850 --> 00:39:38,820
An alternative to this is a new network
interface that we have, which is more on

481
00:39:38,820 --> 00:39:45,400
this XML side or the design of our
experiment configurations, which is meant

482
00:39:45,400 --> 00:39:51,450
to collect data from many users and not
life data. So we had this lecture. So this is

483
00:39:51,450 --> 00:39:55,860
the new lecture hall, by the way. So we
had a lecture where every student got a

484
00:39:55,860 --> 00:40:00,670
spring from us and there was supposed to
build a spring pendulum and we collected

485
00:40:00,670 --> 00:40:05,760
the data from all students and the lecture
hall in realtime on the big screen to

486
00:40:05,760 --> 00:40:13,750
determine the dependency of the frequency
from the mass of the pendulum. And another

487
00:40:13,750 --> 00:40:17,400
example. Just a few days ago, we during
the winter solstice, we asked our

488
00:40:17,400 --> 00:40:22,370
international users to point their phone
at the sun. So we get an angle for the

489
00:40:22,370 --> 00:40:27,520
elevation of the sun and the azimuth from
the magnetometer with a compass. And this

490
00:40:27,520 --> 00:40:31,120
way we could trace the path of the sun
across the earth from all the users. What

491
00:40:31,120 --> 00:40:36,040
each black point with the line is a
contribution from a user. So, yeah, from

492
00:40:36,040 --> 00:40:40,901
this we could, for example, determine the
tilted angle of the earth's axis. OK, so

493
00:40:40,901 --> 00:40:43,810
just example, what you can do is this
network interface, as long as we're able

494
00:40:43,810 --> 00:40:47,660
to set up some server to receive the data,
you can use this network interface. We're

495
00:40:47,660 --> 00:40:52,131
still working on this network interface.
So far it can only do HTTP requests, get

496
00:40:52,131 --> 00:40:58,240
or post. But we are also planning on
implementing Mqtt and other protocols like

497
00:40:58,240 --> 00:41:02,980
this. And the third option is a Bluetooth
connection, which is mostly designed for

498
00:41:02,980 --> 00:41:07,360
sensors. So if you want. If you have some
Bluetooth low energy sensor that you want

499
00:41:07,360 --> 00:41:11,510
to read out, you can use Phyfox. So
there's an example of a Texas Instruments

500
00:41:11,510 --> 00:41:15,390
sensor tech, which has a software which is
not designed for Phyfox. But our file

501
00:41:15,390 --> 00:41:20,330
format is flexible enough to
simply tell Phyfox how to read all the

502
00:41:20,330 --> 00:41:25,920
data and suddenly we've got the sensor
that can run independently from the phone.

503
00:41:25,920 --> 00:41:30,329
And of course you can include your own
projects like this. So there is an example from

504
00:41:30,329 --> 00:41:35,551
actually my institute, because originally I'm in
solid state physicist. So we're working a

505
00:41:35,551 --> 00:41:39,690
lot with graphene and this is a
demonstrated we create that was an ESP 32.

506
00:41:39,690 --> 00:41:46,000
So this is another version of an Arduino, or
Arduino compatibel. What we're doing here.

507
00:41:46,000 --> 00:41:50,460
We're reading out a graphene Hallsensor
and so. It's all similar to the holecenter

508
00:41:50,460 --> 00:41:55,590
of phone, but based on graphene and we can
get life measurements in Phyfox with this.

509
00:41:55,590 --> 00:41:59,590
And so if you have an Arduino project with
which you want to.. from which you want

510
00:41:59,590 --> 00:42:04,280
to send data that is plotted in Phyfox,
you can do it with a bluetooth low

511
00:42:04,280 --> 00:42:08,840
energy interface. But if you have some
patients and maybe wait two more months,

512
00:42:08,840 --> 00:42:12,890
we are working on Arduino library to make
this simpler. So this the entire code, you

513
00:42:12,890 --> 00:42:17,870
would need to read out the analog input
from an Arduino and send it to Phyfox to

514
00:42:17,870 --> 00:42:22,610
be plotted. OK, so this is working right
now. If you cannot wait, you can check it

515
00:42:22,610 --> 00:42:25,310
out on our website. So this is already
available, although it's a work in

516
00:42:25,310 --> 00:42:29,590
progress. The interface will change a bit
still. I would prefer if you want to

517
00:42:29,590 --> 00:42:33,200
start right now, if you contact me so we
can get some feedback and maybe even

518
00:42:33,200 --> 00:42:39,780
design the library also to your needs. So that
we get an idea. So with this, I'm about to

519
00:42:39,780 --> 00:42:47,110
finish. So just a short summary what I'm
hoping I can trigger. Yeah. So if you were

520
00:42:47,110 --> 00:42:52,020
mildly amused, mightily entertained by
this by this talk, check out our Web site

521
00:42:52,020 --> 00:42:55,670
or check out our YouTube channel or
Twitter. We can get some more examples,

522
00:42:55,670 --> 00:43:03,290
what we do with the sensors in the phone.
If you are a teacher, are teachers here?

523
00:43:03,290 --> 00:43:09,130
Quite a few. That's great! And if you want
to use this in class or in a lecture,

524
00:43:09,130 --> 00:43:12,120
check out our Web site phyfox.org. We've
got a database of experiments that you can

525
00:43:12,120 --> 00:43:15,090
do: phyfox.org/experiments .That's then
actually about physics and less about the

526
00:43:15,090 --> 00:43:19,600
hardware where we also demonstrate the
experiments and how they work. If you are

527
00:43:19,600 --> 00:43:24,660
a teacher and has a specific project in
mind. Check out our editor to design your

528
00:43:24,660 --> 00:43:31,610
own set up with which you can do something
specific for a very specific experiment.

529
00:43:31,610 --> 00:43:36,150
phyfox.org/editor. Then if you are working
on arduino project and want to plot

530
00:43:36,150 --> 00:43:40,080
something, you can visit Phyfox.org/arduino,
where you already can access

531
00:43:40,080 --> 00:43:45,010
our library. Although it's not complete as
I said. So maybe wait a little bit or

532
00:43:45,010 --> 00:43:50,290
contact me first. If you have a Bluetooth
low energy device that you want to use or

533
00:43:50,290 --> 00:43:56,100
integrate. You can visit phyfox.org/ble.
If it's about a device that you did not

534
00:43:56,100 --> 00:44:00,060
design yourself, you probably need some
background information about bluetooth low

535
00:44:00,060 --> 00:44:04,870
energy. Should know what a GATT server is
and how characteristics and services, new

536
00:44:04,870 --> 00:44:08,261
ideas and all this stuff and bluetooth
energy works. And it's good to get some

537
00:44:08,261 --> 00:44:13,130
documentation or to be good as reverse
engineering, but in principle I haven't

538
00:44:13,130 --> 00:44:19,980
seen many devices so far which could not
work with phyfox easily. Then if you want

539
00:44:19,980 --> 00:44:26,460
to read the values for another project via
network, visit our website, the wiki on

540
00:44:26,460 --> 00:44:30,830
our website. phyfox.org/wiki, where you
can get information about the rest API and

541
00:44:30,830 --> 00:44:34,870
on your network interface. And finally,
something I would really love if you want

542
00:44:34,870 --> 00:44:39,820
to contribute. If you can write some apps,
I mean you can use a lot of things. The iOS

543
00:44:39,820 --> 00:44:45,510
app is written in swift. The Android
version is written in Java. Our webserver,

544
00:44:45,510 --> 00:44:50,320
of course, has web development and Html in
JavaScript. So if you want to contribute

545
00:44:50,320 --> 00:44:55,800
there. Visit our Web site at a
phyfox.org/source. And we would love to

546
00:44:55,800 --> 00:45:01,800
see some help in development. With this I
finish my talk and I'm looking forward to

547
00:45:01,800 --> 00:45:05,260
any exchange we will have later and any
questions. And I'm just thankful that it

548
00:45:05,260 --> 00:45:09,630
was allowed to talk here and
get so much attention. Thank you.

549
00:45:09,630 --> 00:45:21,310
<i>Applause</i>

550
00:45:21,310 --> 00:45:27,030
Oh, by the way, since it is up there. One
bad news, unfortunately, I can only be

551
00:45:27,030 --> 00:45:32,270
here today. So if you want to talk to me,
try to catch me today. You can also call

552
00:45:32,270 --> 00:45:36,800
me. I actually brought a DECT phone,
but, uh, sorry, only today.

553
00:45:36,800 --> 00:45:42,500
Herald: Oh, my God. So quickly, though, we
have questions now, 15 minutes, then 15

554
00:45:42,500 --> 00:45:47,250
minutes, I think. And then afterwards, you
have to find him and catch him. Thank you,

555
00:45:47,250 --> 00:45:56,410
Sebastian. Questions. Shoot. There is one.
Question: You mentioned aliasing affect

556
00:45:56,410 --> 00:46:02,210
during.. Is it possible to change or modulate
the sampling frequency to actually find

557
00:46:02,210 --> 00:46:08,580
out our frequency above the sampling frequency?
Sebastian: Yeah, that's that's a good

558
00:46:08,580 --> 00:46:13,580
question. Not only because of the of the
alias affect, but also because some

559
00:46:13,580 --> 00:46:17,180
projects also want to reduce the sampling
frequency. It's a little bit tricky

560
00:46:17,180 --> 00:46:22,060
because on both APIs and both IOS and
Android, you cannot specify a target

561
00:46:22,060 --> 00:46:26,190
frequency, you can only specify a
frequency that specific for certain use

562
00:46:26,190 --> 00:46:31,810
case. So for example, you say I need the
accelerometer data, that's which at a rate

563
00:46:31,810 --> 00:46:36,110
that's reasonable for UI changes or at a
rate that's reasonable for games. Right.

564
00:46:36,110 --> 00:46:40,890
Right. That's as fast as possible. So if
you do it for UI, you get something like

565
00:46:40,890 --> 00:46:44,450
let's say two three hertz. We heard something like
this or you doesn't waiting ages before

566
00:46:44,450 --> 00:46:48,460
the screen rotates for games. It's 25 50
hertz something like this. So we can

567
00:46:48,460 --> 00:46:53,270
control the game and fastest is the
data I've just plotted. And Phyfox always

568
00:46:53,270 --> 00:46:57,470
request the fastest we can see and in
Phyfox we have a setting, we can limit the

569
00:46:57,470 --> 00:47:03,020
frequency. Unfortunately, if your
frequency is not simply a multiple, no,

570
00:47:03,020 --> 00:47:06,820
the other way around is. The frequency
given by the device, is not a multiple of the

571
00:47:06,820 --> 00:47:10,541
frequency that you gave. It's not easy to
break it down to the target frequency. So

572
00:47:10,541 --> 00:47:18,200
you usually see some odd cases where
Phyfox tells to group the sensor events

573
00:47:18,200 --> 00:47:24,200
along this to get near this frequency. So
it might not work that well. And

574
00:47:24,200 --> 00:47:27,540
especially if you're looking for the alias
effect. This might really mess up their

575
00:47:27,540 --> 00:47:31,800
alias effect, so you might need to try a
little bit which frequency looks good to

576
00:47:31,800 --> 00:47:35,500
do this. But of course in principle you
can average about multiple values in this

577
00:47:35,500 --> 00:47:42,100
way or simply pick only every end value.
And this way we'd use the frequency. And

578
00:47:42,100 --> 00:47:46,010
yeah, this can be done to our editor or to
the main screen. There's a plus button

579
00:47:46,010 --> 00:47:49,950
with which you can simply expand which
already allows you to set this simple

580
00:47:49,950 --> 00:47:53,530
frequency. Just keep in mind that you
cannot really always get to the

581
00:47:53,530 --> 00:47:57,740
target frequency, right?
Herald: Right. There is another question.

582
00:47:57,740 --> 00:48:01,550
No? Yes. Please.
Question: Hi. Thanks for the cool task.

583
00:48:01,550 --> 00:48:05,930
It's a great app. I love using it in
school. I was wondering if those cool

584
00:48:05,930 --> 00:48:09,790
animations how to sensor types of working
are available.

585
00:48:09,790 --> 00:48:15,390
Sebastian: Sorry. The animation scene.
Yeah. I think I wonder how to do this

586
00:48:15,390 --> 00:48:21,100
best. Before that, I was already thinking
about sharing the slides. Actually, my

587
00:48:21,100 --> 00:48:27,350
talk is space it's just written in HTML in Javascript
it's not easy to control for everyone. That's

588
00:48:27,350 --> 00:48:33,170
why I did not simply upload it. I would if
I would check later, if I can, upload the entire

589
00:48:33,170 --> 00:48:37,260
talk in some way that makes sense either
on our website. I'm not sure if it makes

590
00:48:37,260 --> 00:48:42,490
sense to upload it to the system of the
conference. Still, after the talk, I would

591
00:48:42,490 --> 00:48:49,850
check it, but I am not... I want to share
the slides, but I probably need to add

592
00:48:49,850 --> 00:48:53,750
some documentation on how to use them
because they are not Power point PDF or

593
00:48:53,750 --> 00:48:58,450
Latex generated PDF.
It's handmade.

594
00:48:58,450 --> 00:49:05,060
Herald: You can always cut them out of the
video getting streamed and La la la la la.

595
00:49:05,060 --> 00:49:08,540
Yeah, right.
Question: Just a quick question of the the

596
00:49:08,540 --> 00:49:12,690
axis of the phone. They're like like that
and that distorts us.

597
00:49:12,690 --> 00:49:19,970
Sebastian: So it's not for most phones.
The X-axis is reading directlon. The

598
00:49:19,970 --> 00:49:26,210
Y-axis is upwards along the screen and Z
access, Z-axis depending on your dialect is

599
00:49:26,210 --> 00:49:32,460
perpendicular to the screen. I'd say in
most cases because officially the X-Axis

600
00:49:32,460 --> 00:49:36,000
at least I think I've written this
documentation for Android is along the

601
00:49:36,000 --> 00:49:40,151
natural reading direction of the device.
So if you've got a huge tablet which you

602
00:49:40,151 --> 00:49:45,990
naturally would put in horizontal
alignment, not portrait mode, it might be

603
00:49:45,990 --> 00:49:51,490
that the X-Axis is the long Axis. I have never
seen this myself, but I'm a little bit

604
00:49:51,490 --> 00:49:55,460
careful to say that all these devices have
the same axis, but Z is definitely always

605
00:49:55,460 --> 00:49:59,810
perpendicular to the screen and X and Y are
than the other ones and they are fixed and

606
00:49:59,810 --> 00:50:05,010
usually the short side is the X-Axis.
Herald: Ok. There is one more question

607
00:50:05,010 --> 00:50:10,830
there, please, sir. Take the microphone.
It's next to you. You got it off the

608
00:50:10,830 --> 00:50:13,860
...
Question: Hi, you mentioned the necessity

609
00:50:13,860 --> 00:50:20,760
of the magnetic sensor to to determine the
content orientation. Can you not use past

610
00:50:20,760 --> 00:50:24,510
G.P.S. data and then integrate over the
gyroscope data to get the current

611
00:50:24,510 --> 00:50:27,480
orientation?
Sebastian: <i>Lauthing</i> Mathematically, your

612
00:50:27,480 --> 00:50:34,960
correct, problem is integrating sensor
data is not as simple. I'm often

613
00:50:34,960 --> 00:50:42,080
surprised on what some software
can actually do. If you do it naively

614
00:50:42,080 --> 00:50:45,740
right now I only have an example in mind
for the accelerometer cause it could also

615
00:50:45,740 --> 00:50:49,471
say you can integrate the accelometer data
to get velocity. You can integrate the

616
00:50:49,471 --> 00:50:54,550
velocity to get the displacement of the
phone of the location. If you do this,

617
00:50:54,550 --> 00:50:58,040
we've got a very simple example in our
wiki. Very naiv even one without any

618
00:50:58,040 --> 00:51:03,120
filtering, then just the noise means
that's if there's little arrow, you summit

619
00:51:03,120 --> 00:51:08,270
up integrations, nothing else but
suming up in small steps. You get an

620
00:51:08,270 --> 00:51:13,670
offset error in the velocity. If you
integrate this again, you get an error in

621
00:51:13,670 --> 00:51:17,730
the location with which is growing with
the square of the time. So if you do this

622
00:51:17,730 --> 00:51:22,420
for location and try it out with our naive
approach your phone is supposed to

623
00:51:22,420 --> 00:51:27,420
be 100 meters upwards after about 10
seconds. If you do this for the gyroscope,

624
00:51:27,420 --> 00:51:31,680
it's a little easier because you only
want integration. But still there will be

625
00:51:31,680 --> 00:51:37,210
some drift. I'm not sure about all the
techniques the manufacturers imployed to

626
00:51:37,210 --> 00:51:41,400
filter out any errors. I mean, obviously
the gyroscope is self calibrating

627
00:51:41,400 --> 00:51:45,370
otherwise, it would be pointing in
different direction all the time. And on

628
00:51:45,370 --> 00:51:50,320
some phones I've seen it jumping
when it recalibrates. But if you simply

629
00:51:50,320 --> 00:51:54,900
integrate this, you will certainly get
drift, there's no way that you can get

630
00:51:54,900 --> 00:51:59,130
a fixed position. What I think what they
probably do for most cases, they use the

631
00:51:59,130 --> 00:52:06,290
gyroscope to immediate direct
rotation and then try to fuze it

632
00:52:06,290 --> 00:52:10,180
in some way with the magnetometer
information to keep it fixed so that at

633
00:52:10,180 --> 00:52:13,800
the end you're not pointing the wrong
direction. But the gyroscope itself, only

634
00:52:13,800 --> 00:52:17,660
on its own, is unfortunately only giving
you the rotation rate, not the absolute

635
00:52:17,660 --> 00:52:22,550
rotation in contrast to an actual
gyroscope. The big one that's rotating. So

636
00:52:22,550 --> 00:52:27,530
it's at least not that easy.
That's all I can say.

637
00:52:27,530 --> 00:52:32,760
Herald. Whow? What the bunch of
information, Sebastian? I really love the

638
00:52:32,760 --> 00:52:35,960
.... There is someone else with a
question. I really love your replication.

639
00:52:35,960 --> 00:52:39,250
Actually, it was really immediately fun
to, go.

640
00:52:39,250 --> 00:52:44,010
Question: Thank you so much for a great
application. And my question is, just very

641
00:52:44,010 --> 00:52:50,010
short. Can you also integrate external
sensors through Wi-Fi or is it only to be

642
00:52:50,010 --> 00:52:52,830
early?
Sebastian: No. That's what I meant with

643
00:52:52,830 --> 00:52:59,580
the network connection. Network usually
has Wi-Fi in this case, I'm not sure if it

644
00:52:59,580 --> 00:53:05,230
would work on a conference like this into
the cable. So now you can get the data

645
00:53:05,230 --> 00:53:12,680
through our REST API. Might not be the
fastest thing. Maybe we will add to our

646
00:53:12,680 --> 00:53:19,810
network, our new network functionality,
something that will keep open apart and

647
00:53:19,810 --> 00:53:24,640
push the data in there, so far the best
thing to go is with our rest API.

648
00:53:24,640 --> 00:53:27,390
Question: I was just thinking about the
external sensor connection.

649
00:53:27,390 --> 00:53:32,960
Sebastian: So external? Sorry, I was
thinking a different direction. Actually,

650
00:53:32,960 --> 00:53:35,590
that's a good question. That reminds me of
that, that there's something I wanted to

651
00:53:35,590 --> 00:53:41,700
add. You can use the REST API in theory to
push data in there, but that's only a

652
00:53:41,700 --> 00:53:46,170
parameter in the Url. It's simple a Get/
push off a single value which doesn't get

653
00:53:46,170 --> 00:53:51,690
get you far and which is quite
inefficient. However, within you network

654
00:53:51,690 --> 00:53:57,050
interface you can do requests to other
devices so you can GET request and already

655
00:53:57,050 --> 00:54:01,700
is able to respa Json packet as a
response us to interpret the adjacent

656
00:54:01,700 --> 00:54:05,380
packet as a response. And that's where
adding Mqtt and stuff like this, this is

657
00:54:05,380 --> 00:54:10,000
supposed to go in both directions. But
this is really new. So if you've got

658
00:54:10,000 --> 00:54:14,491
something specific, try if it works or
contact me if it's not working, if you

659
00:54:14,491 --> 00:54:19,770
need some help, if you find the bug. So but
it's supposed to work on your network

660
00:54:19,770 --> 00:54:22,960
stuff. That's there in the configuration. So
the idea of the workflow of all this

661
00:54:22,960 --> 00:54:27,780
connection with specific devices have
something set up like this. You create a

662
00:54:27,780 --> 00:54:32,590
configuration for Phyfox, which in the end
is supplied to the QR code. For example,

663
00:54:32,590 --> 00:54:36,440
the user scans the QR code. And this all
the information, how to communicate with

664
00:54:36,440 --> 00:54:41,610
the device is already supplied. You can
also do this for Bluetooth. That the

665
00:54:41,610 --> 00:54:45,050
device itself provides it to Phyphox.
But in the end it's these configurations

666
00:54:45,050 --> 00:54:50,590
and for the new network interface, it can
also receive data from the network. But so

667
00:54:50,590 --> 00:54:55,790
far only via HTTP.
Question: OK. Thank you.

668
00:54:55,790 --> 00:55:01,960
Herald: I have maybe a last question if no
one else has. What's the next step? What

669
00:55:01,960 --> 00:55:06,370
is your next goal? Because this is a
tremendous successful thing. And you see

670
00:55:06,370 --> 00:55:12,240
the educational purposes. So that's
fantastic, actually, isn't it? It's not

671
00:55:12,240 --> 00:55:17,600
only on university level if you're using
it, that's all around in Germany.

672
00:55:17,600 --> 00:55:20,140
Sebastian: That's not in Germany. It's by
the way another thing you could

673
00:55:20,140 --> 00:55:24,100
contribute. If you're speaking a language
that has been translated into Phyfox is

674
00:55:24,100 --> 00:55:29,310
translated by volunteers and it's already
available, I think in 2010 and 2012, 2013,

675
00:55:29,310 --> 00:55:34,310
14 languages, something around this. So
yeah, but next step I think will be using

676
00:55:34,310 --> 00:55:38,420
the camera because that's another sensor,
broadly speaking, which we are not using

677
00:55:38,420 --> 00:55:43,730
at all, which can do a lot, but we haven't
yet started on this. So lot to do in this

678
00:55:43,730 --> 00:55:45,860
project.
Herald: Super. I'm looking forward to see

679
00:55:45,860 --> 00:55:55,080
you next year then. <i>Laughing, Applause</i>
Sebastian Starks, thank you very much. An

680
00:55:55,080 --> 00:55:57,930
honor and a pleasure to have you.

681
00:55:57,930 --> 00:56:02,340
<i>Postroll music</i>

682
00:56:02,340 --> 00:56:24,000
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